This application claims the benefit of Japanese Patent Application P2002-11, 970, filed on Jan. 21, 2002, the entirety of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a high pressure discharge lamp and an assembly and discharge vessel therefor.
2. Description of the Related Art
A high pressure discharge lamp has a ceramic discharge vessel with two end portions. Sealing members (usually referred to as a ceramic plug) are inserted, respectively, to seal the respective end portions. A through hole is formed in each sealing member. A metal member with an electrode system is inserted in the through hole. An ionizable light-emitting material is introduced and sealed in the inner space of the discharge vessel. Known high pressure discharge lamps include a high pressure sodium vapor and metal halide lamp, the latter exhibiting more superior color coordination. The lamp may be used in high temperature condition by forming the discharge vessel with a ceramic material.
In such discharge lamp, it is necessary to air-tightly seal between the end portion of the ceramic discharge vessel and a member for supporting an electrode system. The ceramic discharge vessel has a main body with a shape of a tube with two narrow ends, or a barrel, or a straight tube. The discharge vessel is made of for example, an alumina sintered body.
A Japanese patent application No. 178,415/1999 (EP 0982278, A1) discloses the following structure. A joining portion is provided between the end portion of a ceramic discharge vessel and a member for supporting an electrode system. The joining portion has joining material contacting the discharge vessel and an intermediate glass layer contacting the supporting member and existing between the supporting member and the joining material. The joining material is composed of a porous bone structure with open pores and made of a sintered product of metal powder. The joining material further has glass phase impregnated into the open pores in the bone structure. Herewith, such joined body has improved air-tightness and resistance against corrosion, so that thermal cycles does not result in the fracture of the joined body.
When the joined structure described above is produced, a porous bone structure is formed on the outer surface of a metal tube made of, for example, molybdenum and the metal tube is then inserted into an opening formed in an end portion of a ceramic discharge vessel. A clearance is formed between the porous bone structure and the inner surface of the vessel. Molten glass is then flown into the clearance and then solidified. The thus produced joined structure has improved air-tightness and resistance against cycles of turning ons and offs.
The inventor has found the following problems in the mass production process of the joined structure. That is, the molten glass may be adhered onto the end face or inner surface of the metal tube and solidified. In this case, the solidified glass may prevent the insertion and fixing of a supporting rod for an electrode into the inner space of the metal tube, so that the production yield may be reduced.
The object of the present invention is to provide a novel high pressure discharge lamp utilizing a ceramic discharge vessel and a conductive member inserted into the opening of the end portion of the vessel, so that the adherence of a joining material onto the end face or inner surface of the conductive member may be prevented.
The present invention provides an assembly for a high pressure discharge lamp. The assembly has a ceramic discharge vessel having end portions and an inner space formed therein to be filled with an ionizable light emitting substance and a starter gas, and the end portion has an inner wall surface facing an opening formed in the end portion. The assembly further has a conductive member having an outer surface and inner surface facing a hollow portion formed therein. The conductive member is inserted in the opening, and a joining layer joins the inner wall surface of the end portion and the outer surface of the conductive member. A recess facing the opening is formed in the end portion, and the recess extends circumferentially with respect to the central axis of the vessel.
The present invention further provides a high pressure discharge lamp having the assembly and an electrode system fixed in the inner space of the vessel.
The present invention further provides a ceramic discharge vessel for a high pressure discharge lamp. The vessel has end portions and an inner space formed therein to be filled with an ionizable light emitting substance and a starter gas. The end portion has an inner wall surface facing an opening formed in the end portion. A recess facing the opening is formed in the end portion and extends circumferentially with respect to the central axis of the vessel.
The inventor has studied the cause of the adhesion 25, 26 (see FIG. 7) of joining material onto the end face 6d and inner surface 6e of a conductive member 6. The inventor has reached the following discovery. That is, molten joining material is flown onto the inner surface 2b of an end portion 2 of a ceramic discharge vessel 1. The molten material tends to wet the end face 6d and inner surface 6e of the conductive member 6, before wetting the inner wall surface 2b of the end portion of the vessel 1. Furthermore, the molten material may be easily absorbed toward the inner space 5 through a clearance between the outer surface 6a of the member 6 and the inner wall surface 2b of the end portion 2 by means of capillary phenomenon.
Based on the above discovery, the inventor has tried to form a recess 3 extending circumferentially with respect to the central axis xe2x80x9cXxe2x80x9d of the vessel 1 on the inner wall surface 2b facing an opening 32 of the end portion 2. When molten joining material is flown into a clearance between the outer surface of the member 6 and inner wall surface 2b of the end portion 2, it is thereby possible to prevent the absorption due to the capillary phenomenon. It is further possible to absorb excess joining material into the recess and to prevent the wetting of the end face and inner surface of the conductive member with the molten joining material.
The effects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art.